<?php
/**
 * <https://y.st./>
 * Copyright © 2018 Alex Yst <mailto:copyright@y.st>
 * 
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program. If not, see <https://www.gnu.org./licenses/>.
**/

$xhtml = array(
	'<{title}>' => "The $a[IRA] mess continues",
	'takedown' => '2017-11-01',
	'<{body}>' => <<<END
<img src="/img/CC_BY-SA_4.0/y.st./weblog/2018/04/27.jpg" alt="Clovers, grass, and more" class="framed-centred-image" width="649" height="480"/>
<section id="IRA">
	<h2>The $a[IRA] mess</h2>
	<p>
		I&apos;ve been unable to communicate directly with the person in charge at my workplace and they don&apos;t seem to actually pay attention to what I say, so it&apos;s been impossible to get through to them.
		They dropped by the workplace today though, so I was able to repeat some things I&apos;d said before, this time in the context of what they&apos;d said.
		Had they listened, that context wouldn&apos;t be needed.
		Anyway, they&apos;re supposedly going to contact support themself to try to get some stuff resolved.
	</p>
</section>
<section id="drudgery">
	<h2>Drudgery</h2>
	<p>
		My discussion post for the day:
	</p>
	<blockquote>
		<p>
			First, let&apos;s get something out there: if it&apos;s able to browse the Internet, it&apos;s not a telephone.
			Telephones don&apos;t do that.
			Rather, modern mobile devices are just pocket computers that come preconfigured to make use of telephony easy.
			Sure, it has the ability to make telephone calls, but so does a laptop or desktop computer.
			You just need the right software and service, just like with a mobile device; the mobile device just has it preinstalled.
			Computers, unlike telephones, are general-purpose computing devices that can perform a multitude of tasks based on the software and hardware provided them.
			A telephone, on the other hand, makes and receives telephone calls and does nothing more.
			Computers, being general-purpose machines, are able to duplicate the functionality of other devices.
			They can run a telephone application, a calculator application, et cetera.
			I actually used an old laptop as a telephone several years ago.
			It isn&apos;t difficult.
			Some (but not many) flip phones are still barely able to be considered telephones, but modern, mini-tablet-like devices are just that: miniature tablet computers.
			Calling that mini tablet in your pocket a telephone is as accurate as calling a wrench a hammer just because you can pound nails into the wall with it.
		</p>
		<p>
			If we&apos;re going to discuss the features of 1G, 2G, 3G, and 4G telephones, we need to be careful not to accidentally include so-called &quot;smartphones&quot;; either that, or we need to discuss not mobile <strong><em>telephones</em></strong>, but instead the supercategory of 1G, 2G, 3G, and 4G mobile <strong><em>devices</em></strong>.
			3G devices and beyond transmit not only voice data, but also Internet data, meaning that there by definition do not exist 3G or 4G telephones.
			For that reason, I&apos;ll discuss mobile devices and not specifically mobile telephones.
		</p>
		<p>
			Mobile devices had, at the time of the writing of the textbook, gone through three generations.
			A fourth was underway back then, and is pretty well established by now.
			I heard a rumour the other day that work on 5G has even begun, though I haven&apos;t looked into it myself.
		</p>
		<p>
			I apologise in advance; I don&apos;t like how my country behaves in regards to standards.
			Quite frankly, we don&apos;t follow the global standards like we should, and it makes me angry.
			I kind of let loose a bit below, as the $a[GSM] versus $a[CDMA] battle in my country drives me up the wall.
			Thankfully, it&apos;s been resolved in 4G, but I&apos;ve never actually had a 4G device, so I&apos;m still stuck in the world of bogus standards competing against legitimate standards.
			I&apos;ve only really used 3G devices due to how most devices on the market are locked-down pieces of junk.
			A limited number of 3G devices have been reverse engineered into something useful, but 4G has been out of my reach.
			From the looks of it, this will be rectified in January, but that&apos;s still some time off.
		</p>
		<h3>First generation</h3>
		<p>
			1G devices transmitted analogue voice data (Tanenbaum &amp; Wetherall, 2011).
			If you have any familiarity with data formats, you know analogue data has some major drawbacks.
			Specifically, it&apos;s subject to heavy degradation.
			<strong>*All*</strong> signals degrade due to imperfections in the transmission material, without exception.
			In digital data, as long as the signal doesn&apos;t degrade too much, the intended signal can be derived from the received signal; the receiver just has to measure the signal against a threshold.
			However, in analogue data, the intended signal at any point be at a multitude of strengths, not just some finite number of strengths such as two.
			Because we have a range of values and not finite points, the received signal has to be taken as is, without any way to even attempt to derive the intended signal from it.
			Every little flaw is just preserved.
		</p>
		<p>
			This generation introduced the concept of cells, which saw continued use in all later generations.
			Cells are small areas each serviced by a tower; mobile devices send signals to and receive signals from the tower, and the tower links into the physical lines connecting to the mobile switching centre.
			(In large networks, there may be many levels of switching centre, with the towers connecting to the outermost level.)
			These switching centres connect to one another over a packet-switched network on more physical lines.
			Of particular note, signal ranges don&apos;t form a neat grid, so either the signal areas have to overlap or some areas must remain dead spots with no service.
			Obviously, the overlapping signal is preferable.
			Because of this overlap, no two adjacent cells can operate on the same frequency, as they&apos;d interfere with one another in the overlapped area.
			As a device&apos;s signal fades, the switching centre knows the device is likely leaving the cell, so the towers of surrounding cells are queried as to the signal strength they experience from the device, the appropriate new cell is chosen, and the device is instructed to change frequencies to use the band of the appropriate cell (Tanenbaum &amp; Wetherall, 2011).
		</p>
		<p>
			The &quot;Advanced Mobile Phone System&quot;, the system used by first-generation devices (which were still actual telephones at this point), divided the frequency band into 1664 simplex (one-way) channels, which were paired to form 832 full-duplex (two-way) channels.
			After accounting for all the overhead channels, such as control channels, paging channels, and access channels, about forty-five simultaneous calls could be in progress in a given cell.
			Devices of this era stored the telephone number as two separate numbers: a 10-bit area code and a 24-bit subscriber number.
			When the device was powered on, it scanned known control channels to find the strongest signal.
			Then, as well as every fifteen seconds afterwards, it broadcast these numbers along with its 32-bit serial number in digital packet form.
			The local switching centre received these packets through the towers, and both recorded the device&apos;s presence and informed the subscriber&apos;s home switching centre.
			A device attempting to place a call sent the intended receiver&apos;s telephone number along with identifying information of the calling device to the tower.
			The switching centre checked to see if it could find that device registered with either its own company&apos;s system or the systems of partner companies, then if found, asked the device using the paging channel if it was still there.
			All devices on the network monitor the paging channel, so the receiver would see the message and respond.
			the switching centre then set up a channel, informed the caller, and put information on a paging channel for the receiver to see, and the receiver would see the call and connect to the designated channel (Tanenbaum &amp; Wetherall, 2011).
			Of particular note, calls between unpartnered companies were not possible at this time.
		</p>
		<h4>Early models</h4>
		<p>
			The textbook seems to classify push-to-talk systems as a type of mobile telephone.
			These systems were similar to the walkie-talkies of today, with the main difference being that there was a central tower used to catch and re-transmit the signal.
			Later, a similar system was used with multi-channel support, which allowed users to not only send and receive at the same time, but also communicate on separate channels from other people, allowing multiple conversations to exist without being heard by people not involved.
			Only twenty-three conversations could be had at once though, so users often had to wait to place a call.
			These early models also had towers that covered a much wider area.
			Not only could fewer calls be placed, but the area of the call count was larger.
			Radios consumed more power too, as they needed to transmit further to reach the central tower (Tanenbaum &amp; Wetherall, 2011).
		</p>
		<h3>Second generation</h3>
		<p>
			Second-generation devices are digital, and digital systems require smaller cells (the book doesn&apos;t specify the reason).
			As such, second-generation service requires more towers than first-generation service.
			Digital data has a number of advantages though.
			In addition to better resistance against degradation, digital data can be compressed and encrypted.
			No longer could handsets eavesdrop on calls not meant for them.
			(That said, it&apos;s widely known that these days, big carriers such as AT&amp;T send your call data to untrusted third parties such as the $a[NSA].
			As calls aren&apos;t end-to-end encrypted, your carrier sees the unencrypted version of the data and can do whatever they like with it.
			Second-generation (or 3G/4G, for that mater) service didn&apos;t make call data secure, it just made it more secure than 1G service.)
			$a[SMS] was also added at this time (Tanenbaum &amp; Wetherall, 2011).
		</p>
		<p>
			$a[GSM] became the global standard, which is used in sane countries.
			A few idiotic countries, such as the United States where I live, didn&apos;t standardise even within their boarders, so devices of this time period couldn&apos;t always switch between carriers.
			$a[GSM] also introduced the concept of a $a[SIM] card (Tanenbaum &amp; Wetherall, 2011), which on most networks, allows you to switch carriers or handsets by simply swapping the $a[SIM] card out.
			If you move your $a[SIM] card to a new device, the network immediately recognises the new device as being the one connected to your line.
			If you put a new $a[SIM] card in your old device, you&apos;d have the new line associated with the old device, allowing you to switch to another provider.
			Again, because the United States is terrible, this didn&apos;t go unmodified here.
			People of my country have to deal with $a[SIM] locks if they&apos;re stupid enough to buy devices directly from carriers instead of buying unlocked third-party devices, such as international variants.
			I&apos;ve also run into a couple companies that wouldn&apos;t allow their $a[SIM] cards to be swapped <strong>*into*</strong> devices.
			Even in an unlocked device, the network refused to recognise the $a[SIM] cards if they weren&apos;t in the original devices.
			Both these companies lost my business because I couldn&apos;t bring my fully-compatible, existing device onto their network.
			I wasn&apos;t going to buy (or use) the locked-down <strong>trash</strong> that they wanted to sell me.
		</p>
		<p>
			With voice data compressed, it doesn&apos;t need to take up the full channel as in 1G service.
			Instead, each channel is split into eight time slots, so multiple devices can broadcast on the same channels at staggered intervals.
			Interestingly, the uplink and downlink occur on the same frequencies, but in different time slots.
			Each slot instance is called a data frame, and eight put together form a $a[TDM] frame.
			Strangely though, each $a[TDM] frame is separated by 8.25 bits worth of space; it&apos;s not even an integer.
			Twenty-six of these $a[TDM] frames form one multiframe, with one $a[TDM] frame reserved for control data and another reserved for future extension of the specification.
			Some multiframes include fifty-one slots instead of twenty-six, though the book doesn&apos;t go into when or why this happens.
			In the larger multiframe, three control channels are present.
			The broadcast control channel is the one that continuously broadcasts the identity of the tower.
			Handsets use this to determine which tower they are getting the strongest signal from.
			Unlike in 1G service, handoff from one tower to the next is aided by the handset, which tells the towers which one it is best able to communicate with at a given time.
			The dedicated control channel is used for updating device location and for patching calls through.
			The third channel is used for paging (announcing a call like from 1G) and requesting/granting access to a slot on the dedicated control channel (Tanenbaum &amp; Wetherall, 2011).
		</p>
		<h3>Third generation</h3>
		<p>
			The third generation introduced general data traffic not related to telephone service, which could be accessed alongside telephone service (Tanenbaum &amp; Wetherall, 2011).
			I&apos;ve never liked the telephone system for a number of reasons.
			For one thing, it&apos;s incredibly poorly implemented, using numeric strings as people&apos;s chat handles, unlike the more-readable format of email addresses or $a[SIP] addresses.
			It also doesn&apos;t allow for namespaces that can be owned by third parties.
			Again, email and $a[SIP] provide this via $a[DNS].
			Telephone numbers used to be like $a[IP] addresses.
			You wouldn&apos;t want to memorise (or keep a list of) the $a[IP] addresses of your favourite websites, would you?
			When telephone number porting was implemented, we ended up with the worst of both an $a[IP]-address-like system (not human readable, not very memorable, and not decentralised) and a $a[DNS]-like system (the numbers mean nothing to the computer, and must be looked up in a lookup table).
			However, there <strong>*is*</strong> one very good thing about the telephone system: it paves the way for the Internet.
			While I don&apos;t pretend to understand why <strong>*anyone*</strong> would want to have telephone service in this day and age (I certainly don&apos;t subscribe to it myself), the simple fact is that the demand for telephone service seems to be the driving force between the establishment of the initial connections over which the Internet travels.
			(I mentioned earlier in this post having used 3G service in the past, but I use tablet lines with no telephony when I subscribe to mobile service.)
			When the Internet was first established, it was done over telephone lines.
			Faster mediums are now more-frequently used, but it was the telephone lines that gave the Internet it&apos;s start.
			And now, mobile telephone service paved the way yet again, initially connecting mobile devices into the telephone network, and later, in the third generation of mobile service, connecting mobile devices to the Internet.
		</p>
		<p>
			According to the book, 3G service is supposed to provide four things: high-quality voice transmission, a messaging system that replaces $a[SMS]; fax service; and email, multimedia service that includes music and video (including films and television video), and Internet access.
			I&apos;m not sure why the messaging service and the multimedia service are intended to be separate from the Internet service though, as these can easily be (and in fact are) provided by a multitude of Internet-based services.
			These services are also supposed to be available globally, though stupid countries such as the United States make that difficult with a lack of standards conformance.
			And finally, these services are supposed to be available via satellite when local towers are unavailable (Tanenbaum &amp; Wetherall, 2011), though I&apos;m pretty sure you need special equipment for that in the actual implementation.
			The required radios aren&apos;t included in most off-the-shelf models in circulation.
		</p>
		<p>
			$a[WCDMA] was based on the $a[CDMA] standard implemented in some countries that didn&apos;t properly commit to the $a[GSM] standard, but unlike $a[CDMA], $a[WCDMA] was used in $a[UMTS], which was intended as the successor of $a[GSM] (Tanenbaum &amp; Wetherall, 2011).
			That made $a[UMTS] the new global standard.
			The United States, like the imbeciles that we are, instead elected to use a competing standard in some places: $a[CDMA]2000.
			Like $a[UMTS], $a[CDMA]2000 was based on 2G $a[CDMA], but unlike $a[UMTS], $a[CDMA]2000 is incompatible with the equipment used in the rest of the world.
			A few other countries use $a[CDMA]2000 as well, but the number of places that use this are very limited.
		</p>
		<p>
			The basic concept $a[UMTS] (and $a[CDMA]2000) is that all the handsets and the tower all broadcast at once.
			There&apos;s no separated time slots.
			It seems like this should be an undecipherable mess and no transmission would be understood, but there&apos;s a method of filtering out the unwanted signals to identify a the single signal you want to listen to.
			Unfortunately, I don&apos;t understand the explanation on how this is done, so I can&apos;t explain it myself.
			I think somehow, having very different signals makes them easier to pick out of the combined signal, so large pseudorandom numbers are used, probably as multipliers before broadcast.
			If someone could explain this better, I would be very appreciative.
			In any case, the basic assumptions that allow such a system to work break down when signals are received by the tower at different strengths.
			Transmission power of handsets therefore needs to be strictly controlled.
			Signals from handsets neat the tower would overshadow signals from handsets far from the tower if nothing was done to compensate, so handsets use the strength of the signal they receive from the tower to determine how strong of a signal they should send.
			If the tower signal is strong, the tower must be nearby, so the device transmits a weak signal to avoid overshadowing distant units.
			If the tower signal is weak, the handset must be far from the tower, so it transmits a strong signal to rival the observed strength of handsets near the tower.
			The towers also send the handsets information to fine-tune their output strength for further signal level control.
			Because multiple signals can be transmitted on the same frequency without becoming hopelessly entangled, adjacent cells are able to reuse the same bands as one another, increasing the amount of frequency range each tower can use.
			This obviously increases the amount of data that can be on the air at once in each cell.
			Another way capacity was improved for 3G service is that sectored antennas were used.
			Signals only need to be transmitted in the direction of the handset the signals are meant for, so those signals don&apos;t need to be transmitted in every direction at once as was done in 1G and 2G towers.
			Additionally, the protocol was designed in such a way that during a handoff, the new tower picks up the duty of supporting the current call before the old tower drops the call.
			Unlike in 2G service, this allows for fewer dropped calls when the handset travels between cells (Tanenbaum &amp; Wetherall, 2011).
		</p>
		<h3>Fourth generation</h3>
		<p>
			At the time the textbook was written, 4G was just beginning to roll out, so not much information is given.
			However, it&apos;s main feature (in my opinion, at least) is that service providers have finally agreed upon a single standard.
			A device purchased anywhere should work on any network.
			Additionally, 4G provides higher data-transfer speeds and direct integration into $a[IP] networks such as the Internet.
			Supposedly, 4G service also offers high service quality for media, but like before, I&apos;m unclear on how this is separate from general high-quality network access (Tanenbaum &amp; Wetherall, 2011).
			To the best of my knowledge, no handset has a media transfer service that exists separately from it&apos;s Internet connection service.
		</p>
		<div class="APA_references">
			<h3>References:</h3>
			<p>
				Tanenbaum, A. S., &amp; Wetherall, D. J. (2011). 2: The Physical Layer. Retrieved from <a href="https://my.uopeople.edu/pluginfile.php/268187/mod_book/chapter/150457/Chapter%202.pdf"><code>https://my.uopeople.edu/pluginfile.php/268187/mod_book/chapter/150457/Chapter%202.pdf</code></a>
			</p>
		</div>
	</blockquote>
</section>
END
);
